1. Field of the Invention
The present invention relates to a color filter and a liquid crystal display device using the same.
2. Description of the Background Art
In a liquid crystal display device capable of displaying color images, a color filter including a large number of red, green and blue colored layers regularly arranged together is provided on the display-surface-side substrate. The pigment dispersion method has been a mainstream method for manufacturing a color filter because the method is superior in terms of heat resistance, light resistance and cost. However, as compared with the dyeing method using dyes, the pigment dispersion method is inferior in terms of the depolarization of pigment particles.
For example, Japanese Laid-Open Patent Publication No. 11-6911 states that color filters manufactured by the pigment dispersion method are inferior in terms of the depolarization, as compared with those manufactured by the dyeing method, because of scattering of light occurring due to pigment particles and surface configuration, that the amount of light transmitted is reduced by the scattering of light, thus failing to obtain sufficient brightness for the same chromaticity, and that the chromaticity of a combination color shifts if the transmittance decreases for even just one of red, blue and green, depending on the degree of scattering. In view of this, a technique has been disclosed in the art in which an ink receiving layer made of a photosensitive resin composition is subjected to a pattern exposure process to form non-colored portions, and a colored ink is applied onto the unexposed portions using an inkjet head to color the unexposed portions, after which the colored portions are subjected to an air flow or vacuum drying, and then the entire ink receiving layer is cured.
Japanese Laid-Open Patent Publication No. 08-171014 is directed to an improvement through yellow added to red and green. Specifically, the gray-scale display is improved through an increase in the contrast ratio of the color filter by using a color resist in which yellow is added to red and green colored compositions while reducing the particle size of the pigment in the colored composition by using a benzimidazolone derivative as the dispersant. However, the publication fails to disclose specific gray-scale display data and fails to describe the chromaticity in a black display.
Japanese Laid-Open Patent Publication No. 2001-188120 discloses a colored composition for a color filter including at least a pigment, a polymer and a solvent, in which the content of a yellow pigment in the pigment component is 30% by weight or more and the relative surface area of the yellow pigment is 70 m2/g or more. The publication states that by optimizing the relative surface area of the yellow pigment, it is possible to form a colored film having a high contrast ratio and to obtain a color filter having a high display quality.
Japanese Laid-Open Patent Publication No. 2001-194658 discloses a liquid crystal display device including a pair of opposing substrates and a liquid crystal material sealed therebetween, with a color filter including red, green and blue color patterns being formed on one substrate, in which an adjustment is made so that CR1/CR2≦.6, where CR1 is the contrast ratio of the color pattern of the highest contrast ratio and CR2 is that of the color pattern of the smallest contrast ratio while the contrast ratio of the panel is 400 or more, thereby improving the color reproducibility.
In recent years, the contrast and the luminance of liquid crystal display device have been increased. This has led to cause a problem that light leakage of a color, e.g., magenta, is observed in a black display, and the magenta color in a black display can be quite conspicuous. This problem is particularly pronounced with liquid crystal display devices having a high contrast ratio and a high backlight brightness, e.g., LCD televisions.
Note that Japanese Laid-Open Patent Publication No. 08-171014, supra, only discloses improvements on the red and green colored layers and fails to give limitations on the blue colored layer. Thus, it is difficult with such a disclosure to realize a desirable black display.